Medium texture detection device

Abstract

A medium texture detection device includes: a radiation optical system that radiates non-coherent light to a sheet-shaped medium which is being transported; and a light reception optical system that receives diffused/reflected light of the non-coherent light from the medium. A surface of the medium has a basic structure for making a change in an intensity of the diffused/reflected light according to a position of the medium in a transport direction of the medium. A visual field of the light reception optical system is set to be equal to or greater than 1/10 times and equal to or less than 4 times of a size of the basic structure.

What is claimed is: 
     
       1. A medium texture detection device comprising:
 a radiation optical system that radiates non-coherent light to a non-printing surface Pb of a sheet-shaped medium which is being transported, wherein the non-printing surface Pb is on an underside of the sheet-shaped medium; and 
 a light reception optical system that receives diffused/reflected light of the non-coherent light from the medium, 
 wherein a surface of the medium has a basic structure for making a change in an intensity of the diffused/reflected light according to a position of the medium in a transport direction of the medium, and 
 wherein a visual field of the light reception optical system is set to be equal to or greater than 1/10 times and equal to or less than 4 times of a size of the basic structure. 
 
     
     
       2. The medium texture detection device according to  claim 1 , wherein the size of the basic structure is a space period indicating a space frequency component that has a maximum real part among space frequency components included in the change in the intensity of the diffused/reflected light. 
     
     
       3. The medium texture detection device according to  claim 1 , wherein the non-coherent light is light with a wavelength of an infrared region. 
     
     
       4. The medium texture detection device according to  claim 1 , wherein the radiation optical system includes
 a light source that emits the non-coherent light, and 
 a light-guiding unit that guides the non-coherent light to the medium, and wherein the light reception optical system includes 
 an optical fiber that receives the diffused/reflected light from the medium through an incidence surface which is one end surface as a light reception surface and exits the diffused/reflected light from an exit surface which is the other end surface, 
 a photosensor that receives the diffused/reflected light emitted from the exit surface and outputs an electric signal according to an intensity of the received diffused/reflected light, and 
 a condensing lens that condenses the diffused/reflected light emitted from the exit surface of the optical fiber toward the photosensor.